First-principles study of direct Z-scheme two-dimensional Janus WTe 2 /XSSe (X = Sn, Hf, Pt) heterojunctions for efficient photocatalytic overall water splitting into hydrogen and oxygen

Abstract Two-dimensional Z-scheme photocatalytic materials have demonstrated considerable potential for solar-driven water splitting, owing to their efficient charge carrier separation and strong redox capabilities. In this work, we employ first-principles calculations to systematically investigate the structural stability, electronic properties, optical response, and photocatalytic performance of three Janus heterostructures: WTe 2 /XSSe (X = Hf, Pt, Sn). The computational results reveal that all three heterostructures are indirect bandgap semiconductors, with bandgap values of 0.17 eV for WTe 2 /HfSSe, 0.085 eV for WTe 2 /SnSSe, and 0.52 eV for WTe 2 /PtSSe. These systems exhibit a direct Z-scheme charge transfer mechanism and possess suitable band edge alignments that straddle the redox potentials required for overall water splitting. Moreover, the built-in electric field at the interface, oriented from WTe 2 to XSSe, effectively promotes the spatial separation of photogenerated electrons and holes. All heterostructures display significantly enhanced light absorption in both the ultraviolet and visible regions, surpassing that of their monolayer components. The predicted solar-to-hydrogen(STH) conversion efficiencies of WTe 2 /SnSSe and WTe 2 /HfSSe exceed 18%,indicating excellent photocatalytic performance. These findings suggest that WTe 2 /XSSe heterostructures are promising candidates for Z-scheme photocatalysts in solar water splitting applications.